Romania’s proposed compressed-air storage project by Hagag Europe and Airengy introduces a new long-duration trading model for SEE. Unlike conventional batteries, which usually target short intraday spreads, salt-cavern compressed-air storage is designed to store electricity for longer periods. In a region where renewable volatility is increasing and grid flexibility remains limited, that distinction matters.
The project uses Romania’s underground salt caverns as natural pressure vessels. Electricity is used to compress air into the caverns. When electricity is needed, the air is released through a system that drives generation. The first phase targets around 200 MWh of storage at an estimated cost of €4.5mn, while the second phase aims for about 25 MW of discharge capacity and 5 GWh of total storage, with total investment estimated near €55mn.
From a trading perspective, this is not a battery substitute. It is a different product. Lithium-ion batteries are highly effective for fast response, frequency regulation and daily price spreads. Long-duration storage can target multi-day price moves, renewable droughts, prolonged system tightness and capacity-backed products. That gives it a potentially different revenue profile.
Romania needs this flexibility because solar and wind growth are moving faster than system adaptation. Grid constraints, high price volatility and limited storage create opportunities for assets that can shift energy across longer periods. Salt-cavern storage could be especially useful during extended low-wind or low-solar periods, or when abundant renewable output needs to be stored beyond the daily cycle.
The project also has industrial logic. Romania has suitable geological formations, a growing renewables pipeline and a power market large enough to test new storage revenue structures. Hagag Europe contributes cavern access, while Airengy brings the storage technology and operational model.
The risk is bankability. Long-duration storage requires clear revenue mechanisms, whether through arbitrage, balancing, capacity payments or contracted flexibility. Without market rules that reward duration, the technology may struggle despite its system value. Romania’s experiment is important because SEE needs more than batteries. It needs a layered storage market, with speed, scale and duration each priced properly.
